migrat, amb ajuda de claude, a sdl3gpu (postfx i crtpi) igual que el JDD

data/shaders/upscale.frag

@@ -0,0 +1,15 @@
+#version 450
+
+// Vulkan GLSL fragment shader — Nearest-neighbour upscale pass
+// Used as the first render pass when supersampling is active.
+// Compile: glslc upscale.frag -o upscale.frag.spv
+//          xxd -i upscale.frag.spv > ../../source/core/rendering/sdl3gpu/upscale_frag_spv.h
+
+layout(location = 0) in  vec2 v_uv;
+layout(location = 0) out vec4 out_color;
+
+layout(set = 2, binding = 0) uniform sampler2D scene;
+
+void main() {
+    out_color = texture(scene, v_uv);
+}